Blood lactate levels during cardiopulmonary bypass for valvular heart surgery

Cardiopulmonary bypass (CPB) is widely used to maintain systemic perfusion and oxygenation during open-heart surgery. Tissue hypoperfusion with resultant lactic acidosis during CPB, may occur during hypothermia, extreme haemodilution, low flow CPB, and excessive neurohormonal activation. There has been no documentation of the correlation between blood lactate level elevations in the perioperative period, and its relation to preoperative New York Heart Association (NYHA) classification and the use of ionotropic support during weaning from CPB, duration of postoperative ventilatory support and perioperative mortality. We studied the perioperative blood lactate levels in 82 patients undergoing valvular heart surgery. Arterial blood samples were collected at different stages of CPB. The observed mean baseline lactate levels were 1.9+/-0.8 mmol/L (normal range of 0.9 to 1.7 mmol/L). The mean circulating lactate levels at 15 min and 45 min after institution of CPB increased to 7.01+/-2.6 mmol/L and 9.92+/-3.5 mmol/L. A progressive decline in the mean lactate level, was seen during rewarming (at 35 degrees C), immediately off-bypass, 24 hours and 48 hours postoperatively with mean lactate levels being 7.01+/-3.2 mmol/L, 4.75+/-1.01 mmol/L, 3.06+/-1.1 mmol/L, and 2.10+/-1.05 mmol/L respectively. Comparison of mean lactate levels in NYHA class I, II, III, and IV patients showed that in the intraoperative period and immediately after CPB, the elevation in lactate levels were statistically significant (p< 0.001) in patients in NYHA Class IV. However the values, in all classes, were similar at 24 and 48 hours after CPB. Also, patients with lactate levels >4 mmol/ L required prolonged inotropic and ventilatory support.